Let’s say I want to define a data class over a generic type, as part of a sealed class so that I can...

# getting-started

[matt tighe]

Let’s say I want to define a data class over a generic type, as part of a sealed class so that I can use it like this

when (result) {
    is SuccessDataClassWithGenericTypeOf<MyGenericType> -> doThings(it)
    is Failed -> doFailedThings(it.failureMessage)
    is Loading -> doLoadingThings
}

Why does the type get erased in this case:

sealed class MyResultType {
    data class SuccessDataClassWithGenericTypeOf<T>(val result: T) : MyResultType()
    object Loading : MyResultType()
    data class Failed(val failureMessage: String) : MyResultType()
}

But not in this case:

sealed class MyResultType<out T> {
    data class SuccessDataClassWithGenericTypeOf<T>(val result: T) : MyResultType<T>()
    object Loading : MyResultType<Nothing>()
    data class Failed(val failureMessage: String) : MyResultType<Nothing>()
}

[Kroppeb]

The type gets erased in both cases.